This proposal addresses the sensitive detection of chromosomal changes such as small translocations, rearrangements or genomic imbalances in apparently normal individuals, benign neoplasia, premalignant lesions, and cancer. Current techniques for full karyotype analysis of individual cells require metaphase cells, and cells in interphase or non-viable cells cannot be analyzed. Many cells that can be obtained from human tumors are not in metaphase. The objective of the proposed research is the development of technologies to support the cytogenetic analysis of small amounts of fresh, fixed or archival tissues regardless of the cells'proliferative stage. A highly sensitive, fluorescence in situ hybridization (FISH)-based technology platform termed Single Cell Arrays (SCAs) will allow the detection of small rearrangements in interphase and metaphase cells by combining the high-resolution DNA in situ analysis with sensitivity in the kb range. This will be achieved by immobilizing cell nuclei on glass slides and controlled stretching of chromatin in specially designed micro-chambers followed by cytogenetic analysis using FISH. The Specific Aims of this R21 feasibility study are 1. Demonstrate the feasibility that interphase cell nuclei can be immobilized in a defined pattern and reproducibly extended for subsequent cytogenetic analysis. We will demonstrate the feasibility of preparing SCAs comprised of individual cell nuclei arranged in a defined pattern inside microscopic reaction chambers and elongated/stretched by a constant force. Importantly, the extent of chromatin stretching will be controlled by cell fixation and adjusting environmental parameters such as buffer, chamber temperature, and humidity, and the force applied to pull the chromatin. 2. Develop an optimized assay for the sensitive, high-resolution cytogenetic analysis of SCAs. We will develop a protocol for a FISH-based multi-locus cytogenetic analysis of SCAs. The assay is expected to provide near kilobase sensitivity for the detection of single copy nucleic acids with a resolution in the order of 10-20 kb, while minimizing the overall loss of DNA. The assay will be tested by analyzing SCAs prepared from different breast or thyroid cancer cell lines. SCAs will become powerful tools in basic and applied/clinical research, where chromosomal changes often affect a cell's phenotype and the fate of its progeny. In clinical practice, for example, such a sensitive assay may support cell classifications, thereby benefiting patients with de novo translocations or premalignant lesions as well as cancer patients. Furthermore, SCAs will allow the analysis of very small samples, regardless of their integrity or cell cycle stage. This will open new avenues for the analysis of small samples like those obtained by fine needle biopsies as well as the analysis of circulating or exfoliated tumor cells. Public health relevance statement: At present, no technology exists to prepare small samples of non-proliferating cells and screen them for karyotypic abnormalities. Highly sensitive, FISH-based assays termed Single Cell Arrays (SCAs) will provide a platform technology with which one can develop a multitude of tests tailored to specific diseases and cell or tissue samples. Due to their versatility, SCAs may become powerful tools in basic and clinical research, thereby benefiting patients with de novo translocations or premalignant lesions as well as cancer patients.